Mexico Outbreak The Latest In String Of Flu Panics

Influenza pandemics, or the threat of them, have set off waves of panic ever since 1918, when 100 million people around the world died from the illness. Science writer Laurie Garrett explains what we know so far about the current outbreak of swine flu in Mexico and offers some historical perspective to host Jacki Lyden.

The swine flu outbreak in Mexico is the latest in a string of influenza panics that have appeared periodically since the great pandemic of 1918. To get some historical context, I talked with science writer Laurie Garrett. Her books include "The Coming Plague," "Newly Emerging Diseases" and "A World Out of Balance."

We started with a basic primer on three key words: outbreak, epidemic and pandemic.

Ms. LAURIE GARRETT (Senior Fellow, Global Health Program, Council on Foreign Relations): Well, those are dicey terms. Everybody has their own way of defining them. But basically, it boils down to it's an outbreak when it's a small cluster of cases. It becomes an epidemic when it goes well beyond that cluster but still within local boundaries, either the nation or immediate region. It becomes pandemic when it jumps continents or certainly goes the full length of one continental area, such as the Americas.

LYDEN: I see. Most flu outbreaks, as we know, Laurie, hit the elderly and young children the hardest, but most of the dead in Mexico are young, vigorous people. Why would that be?

Ms. GARRETT: There could be two possible explanations for that, the good news one and a bad news one. The good news one would be that the vaccine that people got this fall, who did get a flu vaccine, has offered some margin of protection against this virus. And that might mean then that we can just make up huge batches of it and bring this whole thing to a halt.

If that's the case, then that would explain why young adults have not been protected because they generally don't get vaccinated with flu. And the main recommendations here in the United States is for the vaccine to be delivered to vulnerable populations, the elderly and very young children. So that would be the good news explanation.

The bad news explanation would be that this is following a pattern we've seen in the past, particularly in 1918 and with the bird flu in Asia over the last five or six years, where the real killer effect of the infection is not actually the virus directly itself, but rather the immune response to this very foreign, very strange virus that, from the perspective of the body, you've never seen before, and you don't have routine antibody capacity to respond to it.

And so, what happens is if you're actually, ironically, young and vigorous and healthy, you have a very strong immune system, and your immune responds with a nuclear-bomb-like effect against this invading virus and fills your lungs with fluids, actually worsens the situation. And if that is indeed what's going on in Mexico, it's quite worrisome.

LYDEN: Looking at it historically, is there any comparison about this -with this Mexican outbreak and 1918, the great world pandemic?

Ms. GARRETT: Well, Jacki, the big thing about flu and the reason that it's always a problem, and we always have a different flu circulating around the country every single year, is that this is a very, very sloppy virus. It is a large, what's called RNA virus, meaning that its genetics are stored as RNA, not DNA, and it actually has chromosomes, just like humans have chromosomes, except that this virus' chromosomes are really a mess. They're not well-maintained.

And so, when the virus reproduces, literally, its whole genetic material falls apart, and then it absorbs. As it reassembles and makes progeny, it absorbs genetic material from the environment that it's in.

So if it's in a human cell, it picks up little human RNA. If it's in a pig cell, it picks up pig. If it's in a chicken cell, chicken. What we see with this virus that's so unusual and that, as far as we know, has never happened before is that it has picked up genetic material from three different species: chickens, pigs and humans, and mixed them all up.

And in that sense, it is only similar to what we saw in 1918. And what seems to have happened in 1918, although a lot of the scientific work is so new that we're still figuring it all out, is that a virus emerged that circulated around the world as a human flu.

It was dangerous, but not terrible, but then it circulated both through pigs and through horses in the U.S. cavalry that was bivouacked in World War I in Kansas, and something that it picked up, probably from the horses, turned it into the super virulent, horribly deadly strain, which, according to the latest estimates, killed around 100 million people worldwide.

LYDEN: I'm sitting here trying not to be alarmed and reach for a mask. We've seen people in these masks. Do they work?

Ms. GARRETT: The truth is we don't really know what kind of masks work the best for something like influenza, and we don't really know how long you can use any given mask.

LYDEN: So, how else can people protect themselves?

Ms. GARRETT: It seems that the Mexican authorities are taking the logical response, and that is to advise people to stay at home, to avoid congregating in large settings with large numbers of people. And what I've seen in almost every epidemic I've been in is that the worst thing you can do, unless it's a matter of life and death, is go to a hospital.

LYDEN: Science writer Laurie Garrett. She's currently director for the Global Health Program at the Council on Foreign Relations. And she's a former NPR science correspondent.

NPR transcripts are created on a rush deadline by a contractor for NPR, and accuracy and availability may vary. This text may not be in its final form and may be updated or revised in the future. Please be aware that the authoritative record of NPR's programming is the audio.

Correction April 27, 2009

In some broadcasts, we said the swine flu virus combines human RNA and DNA from pigs. In fact, the virus combines RNA from humans and pigs.